Generally, in the case of the light measuring circuit of a camera or the like, the input and the output circuit of the associated operation amplifier are composed as printed circuits, by providing or wiring the circuit elements on the insulated base plate. In the case of such a light measuring circuit, a photovoltaic converting element such as a silicon photo cell is connected, as a light sensing photoelectric converting element, between the inverting and the non-inverting input terminal of the high input impedance operation amplifier. Further, a circuit arrangement having a diode connected to it is used as the impedance element for Log. compression.
When in such circuit, the light amount incident on the light sensing element is very low, the photoelectric current produced in the photovoltaic element is very small. Accordingly, the light measurement error due to the influence of the leak current in the input circuit becomes large and therefore it is difficult to enlarge the practical light measurement range.